If this is your first visit, be sure to
check out the FAQ by clicking the
link above. You may have to register
before you can post: click the register link above to proceed. To start viewing messages,
select the forum that you want to visit from the selection below.

Pit Learning Series: Extinction Level Events

For those of you that are interested in end of the world scenarios, this Ask The Pit session is perfect for you. Iím going to be discussing extinction level events!

Earth has been orbiting the sun for almost 5 billion years. It has been stable enough for life to exist for almost 3 billion years. Stop for a moment and think about how many life forms have lived and died over this massive timescale. Also remember, life started in the microscopic. The Dinosaurs didnít evolve overnight. Microscopic life ruled the proverbial roost for nearly a billion years. At some point in this timeline, life as we know it today (not exactly, but you get the picture) began to emerge and thrive on Earth.

There is an overarching theme of life and death since our planet coalesced out of its planetary nebula. Organisms live, die and become extinct. Over 99% of Earthís organisms are now extinct! If you look back into the fossil record, you begin to see a pattern of extinction. A steady baseline if you will. However, woven into this baseline are some pretty significant spikes in the extinction rate. These are what we call extinction level events. There are 5-7 events over the past 600 million years. Weíll talk about the 5 most readily accepted. First though, Iím going to go over some of the possible causes.

Impact

For those of you that have read my threads before, it should come as no surprise that this is the first and my favorite possible scenario. A large asteroid or comet (5-10 miles in diameter) would completely obliterate a large portion of life on Earth. An impactor this size would leave a crater hundreds of miles across and would vaporize whatever it touched. It would cause a global firestorm that would incinerate almost all combustible material. As terrible as the impact and subsequent earthquakes, tsunamis and firestorms would be, it would only be made worse by the nuclear winter that would result once the dust plume began reentering our lower atmosphere. It would block out the sun, resulting in global cooling and further death of living creatures. You would expect no large mammals to survive. If you have ever read or watched the film adaptation of Cormac Mccarthyís The Road, this is what it might look like if a smaller asteroid were to impact Earth. If this interests you at all, read Luciferís Hammer by Larry Niven and Jerry Pournelle. This is one of my favorite books of all time.

Let me be clear on this one. There is no recorded evidence that this has caused an event in recent history. There are some scientists that believe this could be an explanation for one of the recorded events, but evidence is sparse. Either way, the odds of one of these affecting Earth are extremely small. Earth would have to be right in the sights of a gamma ray burst and a supernova of an average star would need to be within 200 or so light years. A supernova and gamma ray burst are probably related to each other. GRBs are intense, focused jets of gamma rays and are thought to be released when certain stars go supernova. These are the most luminous events in the universe, an indicator of the sheer power. If a gamma ray burst were close enough, the side of the earth facing the burst would be in rough shape. The atmosphere would be eaten away, our oceans would boil and any life would receive a dose of radiation that would kill them a million times over. A supernova would create similar effects on Earth. Without an atmosphere or ozone layer, the Sunís radiation would soon finish us off.

This is by far the worst scenario you can imagine. In the end, it would be 100% fatal for every living thing on Earth.

As you increase the distance, these become less dangerous. Rest in peace, pitites, there are really no stars within a 120** light year radius from Earth that are in danger of going supernova. That doesnít mean that we canít be adversely affected one, though. We have found nitrate ions in Antarctic ice is direct evidence of known Supernovas. These ions form when the gamma rays from one interact with the nitrogen in our atmosphere, converting it to nitrous oxide.

** IK Pegasi is about 150 years and is the absolute best supernova candidate of which we know.

Volcanism

It is thought that several of the recorded events were instigated or partially caused by volcanism in the form of a basalt trap. In this situation, volcanism creates large areas of basalt lava. Continuous coating and recoating over millions of years leaves areas the size of the continental United States (and larger), covered miles deep in basalt lava. These events are several orders of magnitude larger than any volcanic eruptions we have seen in recorded history.It isnít necessarily the lava itself that is so dangerous. It is the gases that are released over the great timescales. Enormous amounts of carbon dioxide and other noxious gases would be released into the atmosphere. This would lead to large temperature fluctuations and a toxic environment on Earth which would inhibit photosynthesis. Once photosynthesis is disrupted, the food chain breaks down.

Super-volcanoes can be another source of extinction. These massive eruptions are 100s of times larger than something like Mt. St. Helenís in 1980. The danger here is the amount of volcanic dust and ash that is ejected into the atmosphere. A direct result would be a volcanic winter that would cool the Earth considerably. Super-volcanoes are not thought to be the cause of any mass extinction, but they are certainly able to create havoc on smaller geographical scales.

We have our own super-volcano in Yellowstone National Park. Scientists believe it is long overdue for an eruption. On average, it seems to erupt once every 640,000 years. We are several thousand years overdue. If it were to erupt, it would cover much of the United States in several feet of ash. It would be a very dangerous situation. The dust you breathe in would effectively turn to concrete in your lungs. Yikes!